<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <title></title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        
        .boxA {
            margin: 70px auto;
            width: 200px;
            height: 200px;
            background-color: blue;
            border: 10px solid #000;
        }
        
        .boxB {
            /* 将盒子模型设置成IE模型 */
            box-sizing: border-box;
            margin: 70px auto;
            width: 200px;
            height: 200px;
            background-color: green;
            border: 10px solid yellow;
        }
    </style>
</head>

<body>
    <div class="boxA">boxA</div>

    <div class="boxB">boxB</div>
</body>

</html>